<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="button" id="btn" onclick="message()" value="提交">
<input type="text" id="text">
<textarea id="txt" rows="20" cols="20"></textarea>

</body>
<script type="text/javascript">
    function message() {
        var message = document.getElementById('text').value;
        document.getElementById('txt').innerHTML+=message;
    }
</script>
</html>